This application claims the benefit of Korean Patent Application No. 2001-15001, filed Mar. 22, 2001, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein.
The present invention relates to chemical vapor deposition methods, and more particularly to methods for chemical vapor depositing ruthenium on a substrate.
The noble metal ruthenium (Ru) is being widely investigated for use in conductive layers of integrated circuits. In particular, layers comprising ruthenium are being investigated for use as the lower (bottom) electrode of integrated circuit capacitors that may be used, for example, in Dynamic Random Access Memories (DRAM).
It is known to fabricate ruthenium layers by sputtering. Ruthenium layers formed by sputtering may have good surface morphology, low leakage and/or low resistance. However, ruthenium layers that are formed by sputtering may have poor step coverage. This poor step coverage may be disadvantageous when forming three-dimensional capacitor electrode structures, to obtain high capacitance, such as a cylinder-type capacitor electrode and/or a fin-shaped capacitor electrode.
It is also known to form a layer comprising ruthenium using Chemical Vapor Deposition (CVD). In chemical vapor deposition, ruthenium is deposited on an integrated circuit substrate, for example on an interlayer insulating layer of an integrated circuit substrate, using a gasified ruthenium source, and a reaction gas, also referred to as a catalyzer. This may produce a ruthenium layer that has good step coverage. Unfortunately, a ruthenium layer formed by chemical vapor deposition may have worse surface morphology than a ruthenium layer formed by sputtering. It, thus, may be difficult to obtain a desired leakage current characteristic or surface resistance using ruthenium layers formed by chemical vapor deposition.
Some embodiments of the invention form a layer comprising ruthenium by chemical vapor depositing a seeding layer comprising ruthenium oxide on a substrate at a chemical vapor deposition flow rate ratio of a ruthenium source to oxygen gas. A main layer comprising ruthenium is chemical vapor deposited on the seeding layer by increasing the chemical vapor deposition flow rate ratio of the ruthenium source to the oxygen gas. Layers comprising ruthenium that are so formed can have good step coverage and good surface morphology.
According to other embodiments of the invention, a chemical deposition rate remains constant above a breakpoint flow rate ratio of the ruthenium source to the oxygen gas, and increases below the breakpoint flow rate ratio. According to these embodiments, chemical vapor depositing a sealing layer is performed by chemical vapor depositing the seeding layer at a chemical vapor deposition flow rate ratio of ruthenium source to oxygen gas that is below the breakpoint flow ratio. The main layer is chemical vapor deposited by increasing the chemical vapor deposition flow rate ratio of the ruthenium source to the oxygen gas to above the breakpoint flow rate ratio.
According to other embodiments, the main layer is deposited by adjusting the flow rate of at least one of the ruthenium gas source and the oxygen gas. According to yet other embodiments, the seeding layer is chemical vapor deposited at a first pressure and at a first oxygen gas flow rate, and the main layer is chemical vapor deposited at a second pressure that is less than the first pressure, and at a second oxygen flow rate that is less than the first oxygen flow rate. In some embodiments, the first pressure is between about 5 Torr and about 50 Torr, and the second pressure is between about 0.1 Torr and about 10 Torr. In yet other embodiments, the first oxygen flow rate is between about 500 sccm and about 2000 sccm, and the second oxygen flow rate is between about 10 sccm and about 300 sccm. In still other embodiments, the seeding layer and the main layer both are chemical vapor deposited at between about 200xc2x0 C. and about 400xc2x0 C. In yet other embodiments, the chemical vapor depositing a seeding layer is performed at higher temperature than the chemical vapor depositing the main layer.
Other embodiments of the invention form a layer comprising ruthenium by performing chemical vapor deposition using a ruthenium source and oxygen gas at a chemical vapor deposition flow rate ratio of the ruthenium source to the oxygen gas. The flow rate ratio of the ruthenium source to the oxygen gas then is increased. Yet other embodiments can provide temperatures, pressures and/or flow rates that were described above.
Still other embodiments of the present invention form a layer comprising ruthenium by first performing chemical vapor deposition using a ruthenium source and oxygen gas at a chemical vapor deposition rate that is below a breakpoint where the chemical vapor deposition rate remains constant. Chemical vapor deposition then is performed using a ruthenium source and oxygen gas at a chemical vapor deposition rate that is above the breakpoint. In some embodiments, the chemical vapor deposition rate that is below the breakpoint is substantially higher than the constant chemical vapor deposition rate. Pressures, flow rates and/or temperatures may be provided as was described above. Accordingly, ruthenium layers having good step coverage and good surface morphology may be obtained. Thus, if the layer comprising ruthenium is formed on an underlying layer having a trench, a thin ruthenium layer can be uniformly formed on the sidewalls of the trench, without exposing the underlying layer.